Structural and optical characterization of ZnO thin films for optoelectronic device applications by RF sputtering technique

Abstract

This work reports structural and optical study of ZnO thin films grown over p-type silicon (Si) and glass substrates by RF magnetron sputtering technique. Surface morphological and optical properties of thin film have been studied using X-ray Diffraction (XRD), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray (EDX), ellipsometry and photoluminescence (PL) spectroscopy. Strong diffraction peak (002) obtained from XRD spectra of ZnO thin film indicates a preferential growth of single crystalline thin film along the c-axis oriented phase of hexagonal wurtzite structure. Surface morphological feature reveals uniform growth of undoped ZnO thin film over the substrate. Different important microstructural parameters for the film such as grain size, lattice parameters, defect density, stress and strain have been obtained. Optical properties such as transmittance, reflectance, absorption coefficient, refractive index and dielectric constant for a spectral range of 300–800nm have been evaluated. A good optical transmittance of 83–92% has been observed for visible region, and the optical bandgap of ZnO films was found to be 3.23eV. Energy Loss Function (ELF) and photoluminescence (PL) spectra for ZnO thin film has also been analyzed and reported.